Electronic Circuit for a Microphone and Microphone

ABSTRACT

An electronic circuit for a microphone and a microphone are disclosed. In an embodiment, the electronic circuit includes a sigma-delta modulator having a configurable resolution and a mode selector, wherein the sigma-delta modulator is selectively operable in at least two operation modes and the mode selector is configured to determine a desired operation mode dependent on an externally provided control signal and to select the resolution of the sigma-delta modulator according to the determined operation mode.

This patent application is a national phase filing under section 371 ofPCT/EP2015/073416, filed Oct. 9, 2015 which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The invention relates to an electronic circuit for a microphone.Furthermore, the invention relates to a microphone comprising theelectronic circuit. The microphone may be fabricated in MEMS(micro-electrical-mechanical systems) technology.

BACKGROUND

Digital microphones for modern portable devices like smart phones,tablets, cameras, laptops need to handle different scenarios. Forexample, the digital microphones are used for recording voice commandsas well as high-quality videos. Recording voice commands is alow-performance application with reduced requirements for bandwidth anddynamic range. But the microphone has to run continuously in this case,so that power consumption is critical in terms of not draining a batteryof the portable device. In the case of high-quality videos audio qualityis most critical while the requirement on power consumption is not socritical.

SUMMARY OF THE INVENTION

Embodiments of the invention provide an electronic circuit and amicrophone with a configurable performance and power consumption.

According to a first aspect, the embodiments of invention aredistinguished by an electronic circuit for a microphone. The electroniccircuit may comprise a sigma-delta modulator having a configurableresolution and a mode selector. The sigma-delta-modulator is selectivelyoperable in at least two operation modes. The mode selector may beconfigured to determine a desired operation mode dependent on anexternally provided control signal and to select the resolution of thesigma-delta modulator according to the determined operation mode.

This has the advantage that the electronic circuit can be reconfiguredin a flexible and economical way in terms of chip area requirements,complexity and power consumption. Devices which mainly contribute tochip area requirements and power consumption in the electronic circuitfor the microphone are a preamplifier, the sigma-delta modulator and apower management unit comprising, for example, a bandgap, an internalvoltage regulator etc. The sigma-delta modulator is designed to work intwo or more operation modes. The dynamic range of the sigma-deltamodulator can be set to different values depending on the operationmode. The configurable resolution relates to the Signal-to-Noise-Ratio(SNR). The mode selector is configured to determine a desired operationmode dependent on the external control signal and to set the operationmode of the reconfigurable circuit units of the electronic circuit, inparticular the sigma-delta modulator. In this way the performance andpower consumption may easily be adjusted according to givenrequirements.

According to an embodiment of the first aspect, the sigma-deltamodulator comprises a first sigma-delta modulator and a secondsigma-delta modulator, wherein the first sigma-delta modulator and thesecond sigma-delta modulator are cascadable. In this way different kindsof sigma-delta modulators can easily be configured.

According to a further embodiment of the first aspect, the sigma-deltamodulator is operable in a first operation mode and in a secondoperation mode, wherein in a first operation mode of the sigma-deltamodulator only the first sigma-delta modulator or the second sigma-deltamodulator is used to provide a digital output signal on an output of thesigma-delta modulator with a resolution of n bits and wherein in asecond operation mode of the sigma-delta modulator the first sigma-deltamodulator and the second sigma-delta modulator are cascaded such thatthe digital output signal on the output of the sigma-delta modulator isprovided with a resolution of m bits. Herein m is higher than n. In thesecond operation mode a first output signal provided on the output ofthe first sigma-delta modulator and a second output signal provided onthe output of the second sigma-delta modulator are combined. In this waya higher-order noise shaping may be reached and a higher resolution, ofthe digital output signal provided on the output of the sigma-deltamodulator may be reached in the second operation mode.

According to a further embodiment of the first aspect, the sigma-deltamodulator is configured to run in the first operation mode and in thesecond operation mode with different clock frequencies. This allows forfurther adjusting the dynamic range and the power consumption of themicrophone.

According to a further embodiment of the first aspect, the sigma-deltamodulator is configured to run in the first operation mode with a lowerclock frequency than in the second operation mode. Thus, the dynamicrange and the power consumption in the first operation mode can befurther reduced.

According to a further embodiment of the first aspect, the firstsigma-delta modulator and the second sigma-delta modulator comprise thesame modulator architecture. In this way development and productioncosts may be reduced.

According to a further embodiment of the first aspect, the electroniccircuit comprises a preamplifier for processing an electrical inputsignal of the electronic circuit. The preamplifier comprises aconfigurable supply current and is selectively operable in at least twooperation modes. The mode selector is configured to select the supplycurrent of the preamplifier according to the determined operation mode.Preferably, the supply current of the preamplifier is lower when thesigma-delta modulator operates in the low resolution mode. This allowsfor a further adjustment of the dynamic range and the power consumptionof the electronic circuit and microphone.

According to a further embodiment of the first aspect, the electroniccircuit comprises a configurable power management unit for providing atleast one supply voltage to the sigma-delta modulator and/or thepreamplifier. The power management unit is configured to provide atleast one configurable supply voltage and is selectively operable in atleast two operation modes. The mode selector is configured to select atleast one supply voltage provided by the power management unit accordingto the determined operation mode. Preferably, the output supply voltageor supply voltages of the power management unit are lower when thesigma-delta modulator operates in the low resolution mode. This allowsfor a further adjustment of the dynamic range and the power consumptionof the electronic circuit and microphone.

According to a further embodiment of the first aspect, the mode selectorcomprises a frequency discriminator and the externally provided controlsignal is a clock signal. This allows for a cost-effective production ofthe electronic circuit.

According to a further embodiment of the first aspect, the mode selectorcomprises a memory being configured for setting the resolution of thesigma-delta modulator and/or the supply current of the preamplifierand/or the at least one supply voltage provided by the power managementunit.

According to a second aspect, the invention is distinguished by amicrophone comprising a transducer (MEMS) and an electronic circuitaccording to the first aspect.

The electronic circuit may comprise any structural and functionalfeatures as described above. Features described with respect to themicrophone are also disclosed herein with respect to the electroniccircuit and vice versa, even if the respective feature is not explicitlymentioned in the context of the specific aspect.

According to an embodiment of the second aspect, the transducer isfabricated in micro-electrical-mechanical systems technology. Thetransducer may comprise a capacitor. In particular, an acoustical inputsignal may result in a change of capacitance of the transducer.Accordingly, the microphone may be a condenser or capacitor microphone.The transducer may comprise a diaphragm and one or more back-plates.

According to a third aspect, the invention is distinguished by a methodof operating the microphone according to the second aspect, the methodcomprising the steps of selecting the first or second mode and operatingthe microphone in the selected mode.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, refinements and expediencies will become apparent fromthe following description of the exemplary embodiments in connectionwith the figures. These are as follows:

FIG. 1 is a block diagram of a first exemplary embodiment of amicrophone; and

FIG. 2 is a block diagram of a second exemplary embodiment of amicrophone.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 shows a schematic diagram of a microphone 1 comprising anelectronic circuit 5. The electronic circuit 5 may be anapplication-specific electronic circuit (ASIC). The electronic circuit 5may be fabricated as a die.

The microphone 1 may comprise a transducer 10, in particular a MEMStransducer, for converting an acoustical input signal into an electricalsignal. As an example, the transducer 10 may comprise a semiconductormaterial such as silicon or gallium arsenide. The transducer 10 maycomprise a diaphragm and one or more back-plates. As an example, thedistance between the diaphragm and a back-plate may be in a range of 1μm to 10 μm. The transducer 10 may be configured as a differentialtransducer or as a single-ended transducer, for example.

The microphone 1 may comprise a MEMS die and an ASIC die comprising theelectronic circuit 5. The shown electronic circuit 5 may also be usedwith transducers other than a MEMS transducer. The microphone 1 may beused in a headset, for example.

The transducer 10 is electrically connected to the electronic circuit 5.In particular, the electronic circuit 5 may process a signal of thetransducer 10.

The electronic circuit 5 comprises, for instance, a pre-amplifier 40, afilter 50, a sigma-delta modulator 20, a power management unit 60 and amode selector 30.

The sigma-delta modulator 20 receives a signal, preprocessed by thepreamplifier 40 and optionally by the filter 50, from the transducer 10and provides a digital output signal DATA on an output of the electroniccircuit 5.

The sigma-delta modulator 20 comprises a configurable resolution and isselectively operable in at least two operation modes dependent on anexternally provided control signal Ctrl.

For instance, the sigma-delta modulator 20 comprises a first sigma-deltamodulator 21 and a second sigma-delta modulator 22, wherein the firstsigma-delta modulator 21 and the second sigma-delta modulator 22 arecascadable.

The sigma-delta modulator 20 may comprise a multistage noise shaping(MASH) architecture.

The first sigma-delta modulator 21 and the second sigma-delta modulator22 may each comprise a second order modulator. The first and the secondsigma-delta modulator 21, 22 may be configured as a continuous-timesigma-delta modulator comprising a second order continuous-timesigma-delta modulator.

Such a second order continuous-time sigma-delta modulator comprises twomodulator stages 211, 212 each with an analog integrator, weightingelements for differently weighting an input signal and a feedback signaland a difference element for providing a difference signal of the inputsignal and the feedback signal on an input of the analog integrator.

The first sigma-delta modulator 21 and the second sigma-delta modulator22, for instance, comprise each a clocked quantizer 220 providing aconverter output signal on its output and a clocked digital-to-analogconverter 230 for providing an analog feedback signal to the input ofthe respective modulator stages 211, 212.

In a first operation mode of the sigma-delta modulator 20 thesigma-delta modulator 20 is configured such that only the firstsigma-delta modulator 21 is used to provide a digital output signal DATAon an output of the sigma-delta modulator 20 with is used to provide adigital output signal DATA on an output of the sigma-delta modulator 20with a resolution of n bits, wherein the resolution relates to the SNR.In this way a second-order noise shaping with, for instance, a −40dB/dec slope may be reached.

In a second operation mode of the sigma-delta modulator 20 thesigma-delta modulator 20 is configured such that the second sigma-deltamodulator 22 and the first sigma-delta modulator 21 are cascaded suchthat the digital output signal DATA on the output of the sigma-deltamodulator 20 is provided with a resolution of m bits, wherein m ishigher than n. In this way a fourth-order noise shaping with, forinstance, a −80 dB/dec slope may be reached.

In the second operation mode the resolution of the digital output signalDATA of the sigma-delta modulator 20 is higher than in the firstoperation mode. In the second operation mode an output of the secondsigma-delta modulator 22 is coupled to an input of the first sigma-deltamodulator 21. Furthermore, a second output signal HMB provided on theoutput of the second sigma-delta modulator 22 and a first output signalLMB provided on the output of the first sigma-delta modulator 21 arecombined, for example, by a recombination filter 80.

The purpose of the recombination filter is to cancel the quantizationnoise of the second sigma-delta 22 modulator based on the output of thefirst sigma-delta 21 modulator.

The first output signal LMB and the second output signal HMB are, forinstance, are 1-bit-signals. The number of bits at the output of therecombination filter 80 depends on the operation mode. For instance, inlow-mode where the first output signal LMB alone is used, therecombination filter 80 output, equals the recombination filter 80input. This may be realized by bypassing the recombination filter 80.

In high-mode, the first sigma-delta modulator 21 and second sigma-deltamodulator 22 input are both input to the recombination filter 80. But,for instance, the output may be not 2-bit but actually 3-bit as thereare 5 output levels, thus requiring 3 bits. This is due to the filteringoperation of the recombination filter 80. In high mode the SNR isimproved, since the quantization noise of the modulator is 4th ordernoise shaped by the two 2nd order modulators.

Furthermore, the sigma-delta modulator 20 may be configured to run inthe first operation mode and the second operation mode with differentclock frequencies. This allows for further adjusting the dynamic rangeand the power consumption of the microphone 1.

The mode selector 30 of the electronic circuit 5 is configured to selectthe resolution of the sigma-delta modulator 20 dependent on theexternally provided control signal Ctrl.

The preamplifier 40 of the electronic circuit 5 is configured to processan electrical input signal of the electronic circuit 5 provided, forexample, by the transducer 10.

Preferably, the preamplifier 40 comprises a configurable supply currentand is selectively operable in at least two operation modes dependent onthe externally provided control signal Ctrl. In this regard, the modeselector 30 is further configured to select the supply current of thepreamplifier 40 dependent on the selected operation mode.

The power management unit 60 is configured for providing at least onesupply voltage VDD1, VDD2 to the sigma-delta modulator 20 and/or thepreamplifier 40. The power management unit 60 is configured to provideat least one configurable supply voltage VDD1, VDD2 and is selectivelyoperable in at least two operation modes. In this regard, the modeselector 30 is configured to select the at least one supply voltageVDD1, VDD2 provided by the power management unit 60 according to thedetermined operation mode.

The mode selector 30 may be configured to control a setting of givenconfiguration switches S1, S2, S3 of the electronic circuit 5 byproviding a mode control signal opmod dependent on the externallyprovided control signal Ctrl. The electronic circuit 5 may comprise suchconfiguration switches S1, S2, S3 for coupling and decoupling the firstand second sigma-delta modulator 21, 22 and one or more configurationswitches in a switched resistor array (not shown in FIG. 1) of thepreamplifier 40 for adjusting the supply current of the preamplifier 40.

The electronic circuit 5 and consequently the microphone 1 may beoperable in a second mode, which may be a high resolution mode, whereinthe resolution of the digital output signal DATA of the sigma-deltamodulator 20 is high. Furthermore, the supply current of thepreamplifier 40 may be increased, thus generating lower noise and lowerdistortion. The sigma-delta modulator 20 may by clocked with a higherfrequency, for instance 4 MHz. This leads to fourth-order noise shapingand higher SQNR, but also to higher current consumption.

The electronic circuit 5 and consequently the microphone 1 may also beoperable in a first mode, which may be a low-power mode, wherein theresolution of the digital output signal DATA of the sigma-deltamodulator 20 may be low, and the supply current of the preamplifier 40may be reduced, for example, to 20% in comparison to the second mode.The sigma-delta modulator 20 may by clocked with a lower frequency, forinstance 700 kHz. This leads to second-order noise shaping and low powerconsumption.

The mode selector 30 may comprise a frequency discriminator, and theexternally provided control signal Ctrl may be a clock signal. Thefrequency discriminator may use a given frequency threshold value forsetting the first or the second operation mode. For instance, if thefrequency of the clock signal is lower than the given frequencythreshold, the mode selector 30 may set the first operation mode. If thefrequency of the clock signal is higher than or equal to the givenfrequency threshold, the mode selector 30 may set the second operationmode.

Alternatively or additionally the mode selector 30 may comprise a memory90 as shown in FIG. 2. The memory 90 may be configured for setting theelectronic circuit 5 in the first or second mode. In particular, thememory 90 may be programmable for selecting one of the modes. The memory90 is, for instance, configured for setting the resolution of thesigma-delta modulator 20 and/or the supply current of the preamplifier40 and/or the at least one supply voltage VDD1, VDD2 output by the powermanagement unit 60.

The memory 90 may comprise a control input and a clock input. The memory90 is programmable by accessing the control input from the outside, inparticular via a control pin. Depending on the input signal provided tothe control input, the memory 90 switches the electronic circuit 5 towork in a first or second mode. The memory 90, for instance, comprises aone-time programmable memory.

1-13. (canceled)
 14. An electronic circuit for a microphone, theelectronic circuit comprising: a sigma-delta modulator having aconfigurable resolution and a mode selector, wherein the sigma-deltamodulator is selectively operable in at least two operation modes andthe mode selector is configured to determine a desired operation modedependent on an externally provided control signal and to select theresolution of the sigma-delta modulator according to the determinedoperation mode.
 15. The electronic circuit according to claim 14,wherein the sigma-delta modulator comprising a first sigma-deltamodulator and a second sigma-delta modulator, and wherein the firstsigma-delta modulator and the second sigma-delta modulator arecascadable.
 16. The electronic circuit according to claim 15, whereinthe sigma-delta modulator is operable in a first operation mode and in asecond operation mode, wherein, in a first operation mode of thesigma-delta modulator, only one of the first sigma-delta modulator andthe second sigma-delta modulator is used such that a digital outputsignal on an output of the sigma-delta modulator is provided with aresolution of n bits, and wherein, in a second operation mode of thesigma-delta modulator, the first sigma-delta modulator and the secondsigma-delta modulator are cascaded such that the digital output signalon the output of the sigma-delta modulator is provided with a resolutionof m bits, wherein m is higher than n.
 17. The electronic circuitaccording to claim 15, wherein the first sigma-delta modulator and thesecond sigma-delta modulator comprise the same modulator architecture.18. The electronic circuit according to claim 14, wherein thesigma-delta modulator is configured to run in a first operation mode andin a second operation mode with different clock frequencies.
 19. Theelectronic circuit according to claim 14, wherein the sigma-deltamodulator is configured to run in a first operation mode with a lowerclock frequency than in a second operation mode.
 20. The electroniccircuit according to claim 14, further comprising a preamplifier forprocessing an electrical input signal of the electronic circuit, whereinthe preamplifier comprises a configurable supply current and isselectively operable in at least two operation modes, and wherein themode selector is configured to select the supply current of thepreamplifier according to the determined operation mode.
 21. Theelectronic circuit according to claim 20, wherein the mode selectorcomprises a memory being configured for setting the supply current ofthe preamplifier.
 22. The electronic circuit according to claim 14,further comprising a configurable power management unit for providing atleast one supply voltage to the sigma-delta modulator, wherein the powermanagement unit is configured to provide at least one configurablesupply voltage and is selectively operable in at least two operationmodes, and wherein the mode selector is configured to select at leastone supply voltage provided by the power management unit according tothe determined operation mode.
 23. The electronic circuit according toclaim 14, wherein the mode selector comprises a frequency discriminatorand the externally provided control signal is a clock signal.
 24. Theelectronic circuit according to claim 14, wherein the mode selectorcomprises a memory being configured for setting the resolution of thesigma-delta modulator.
 25. A microphone comprising: the electroniccircuit according to claim 14; and a transducer.
 26. The microphoneaccording to claim 25, wherein the transducer is a MEMS(Micro-Electrical-Mechanical Systems) device.
 27. The microphoneaccording to claim 25, wherein the electronic circuit comprises apreamplifier for processing an electrical input signal of the electroniccircuit, wherein the preamplifier comprises a configurable supplycurrent and is selectively operable in at least two operation modes, andwherein the mode selector is configured to select the supply current ofthe preamplifier according to the determined operation mode.
 28. Themicrophone according to claim 27, wherein the electronic circuit furthercomprises a configurable power management unit for providing at leastone supply voltage to the sigma-delta modulator, wherein the powermanagement unit is configured to provide at least one configurablesupply voltage and is selectively operable in at least two operationmodes, and wherein the mode selector is configured to select at leastone supply voltage provided by the power management unit according tothe determined operation mode.
 29. A method for operating the microphoneaccording to claim 24, the method comprising: selecting a first mode ora second mode; and operating the microphone in the selected mode.